Giant hogweed is giant problem for British Columbia

Scott Sutherland

GeekquinoxJuly 25, 2013

It might have a funny name — actually, it has several funny names, including giant cow parsnip and cartwheel-flower — but giant hogweed is proving to be no laughing matter as it creeps its way across the country. Officials in B.C.'s Lower Mainland got an unpleasant surprise this month as removal teams have found the population of the highly-invasive plant has doubled since last year.

In 2011, the state horticulturist of Maine gave a good description of the plant — "Queen Anne's lace on steroids." It does look like the familiar weed — only this giant grows up to 5.5 metres tall and can sport flower-heads about a metre wide. Those massive flowers can produce up to 120,000 winged seeds, which take several years to germinate — but that's fine for the plant as the seeds remain viable in the soil for up to 15 years.

It's pretty clear why even one of the plants can turn into a very long headache for provinces trying to fight the invader.

Unfortunately, the weed fights back. The sap of giant hogweed, housed in the 5-to-10 cm diameter stem, leaves, flowers and roots, is a phototoxin. Any skin that it lands on which is then exposed to sunlight may turn red and start to itch. It can continue to burn and form blisters over the next 48 hours, resulting in purplish scars that can last for years.

Anecdotal reports also suggest contact with the eyes can cause temporary, or even permanent, blindness. Merely brushing against a broken leaf, or handling mowing equipment that contacted a plant, can expose you to enough sap to make you a very unhappy gardener or hiker. The National Invasive Species Working Group feels the risk is significant enough that it recommends a trip to the hospital if you believe you've been affected by the sap.

So disposal of the weed, then, is a tricky business. Most invasive species councils across the country recommend land owners contact professional exterminators to remove the plant if they find it on their property. Parts of the plant have to be handled carfully, for obvious reasons, but officials are also eager to prevent the monstrous flowers from spilling seeds everywhere during disposal. If you spot it on public land - giant hogweed is fond of ditches, streams and roadsides — you can contact your province or territory to let them know. You won't be alone; in a CBC News report, Jennifer Grenz of the Invasive Species Council of B.C. said the Council has been getting 80 calls a day since June.

While you're waiting to get through, you can enjoy hold music by Genesis, with The Return of the Giant Hogweed: "Strike by night! They are defenceless. They all need the sun to photosensitize their venom."

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